Look at baby Banks go!
In the video, the "Younger" star, 31, and her 7-year-old son, Luca (with ex-husband Mike Comrie), cheer on baby Banks as she crawls across the floor toward them.
"Come on! Get your brother," Duff tells her baby.
"You almost got me!" Luca sweetly adds to his little sis.
When Banks finally reaches the pair, her mom celebrates, gushing, "Yay, Baby! Good job!"
Duff captioned the cute clip, "We got a mover."
Banks' proud dad, musician Matthew Koma, was just as touched. "My family," he wrote in the comments.
The adorable video comes a day after Duff shared a precious close-up of her giggly little girl. "If this face doesn’t make you smile well ... you're doomed," she wrote.
Koma revealed the happy news by sharing two photos of his bride-to-be showing off her gorgeous ring. "I asked my best friend to marry me," he wrote in the caption.
Duff shared the same pics on her own page, gushing, "He asked me to be his wife."